Lubricant compositions



United States Patent Ofi ice 2,795,548 Patented June 11, 1957 LUBRICANT COMPOSITIONS John R. Thomas, Albany, and Oliver L. Harle, Berkeley, Calif., assignors to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application June 29, 1954, Serial No. 440,264

9 Claims. (Cl. 252-4945) This invention relates to novel lubricant compositions. More particularly, the invention is concerned with novel lubricating oil compositions having improved oxidation and corrosion inhibiting properties. 7

Lubricating oils generally have a tendency to deteriorate due to oxidation and form decomposition products which are corrosive to metals. Since lubricating oils in use today almost invariably come into contact with metal surfaces, the problem of overcoming oxidation and corrosion is considered to be one of major importance. Operating conditions encountered in modern internal combustion engines in which these oils are commonly employed involve increased temperatures, higher speeds and reduced clearances which tend to promote decomposition and the formation of corrosive products. Furthermore, these engines generally employ alloy metal bearings which, besides their possible catalytic effect on the decomposition of the hydrocarbon type mineral lubricatings oils, are easily corroded and this, in turn, has seriously accentuated the oxidation and corrosion problems in mineral lubricating oils.

Inhibitors have been added to lubricating oils to improve their resistance to decomposition and avoid corrosivity. Mineral lubricating oils for internal combustion engines, due to the severity of their service, have also been compounded with additional agents such as wear inhibitors, sludge inhibitors and detergents to loosen and suspend products of decomposition and counteract their effect. Unfortunately, many of these agents may adversely alfect the efiiciency of the oxidation and corrop sion inhibitors and it is a problem to find inhibitors which will function in combination with them. Furthermore, some of the most eliective oxidation and corrosion inhibitors contain active sulfur and are, therefore, extremely corrosive to silver and similar metals which are subject to attack by active sulfur. These types of metals, although once not so widely used in contact with lubricating oils and therefore considered to constitute only a minor problem, are being increasingly employed today.

Particularly in certain important classes of internal combustion engines as, for example, marine and railroad diesel engines, silver metal-containing bearings are more and more common and the problem of providing proper lubrication for them is one of major importance.

It is, therefore, a general object of this invention to provide lubricating oil compositions having improved antioxidant and anticorrosion properties.

A more particular object of the invention is to provide lubricating oil compositions which are noncorrosive to silver and similar metals.

Another more particular object is the provision of mineral lubricating oil compositions in which the tendency to corrode alloy bearings of internal combustion engines has been inhibited.

A further and somewhat related object is to provide compounded mineral lubricating oil compositions having improved anticorrosion properties without adversely atfecting the stabilizing, deterging and lubricating qualities of the hydrocarbon oil composition.

Another and still more particular object of the invention is the provision of mineral lubricating oil compositions which are noncorrosive to silver metal-containing bearings of the type employed in railroad diesel engines.

Additional objects of the invention will become apparent from the description and claims which follow:

In the accomplishment of the above objects, it has been found that compositions comprising an oil of lubricating viscosity and a complex of boric acid with a member of the group consisting of glycols and polyhydroxy benzenes have greatly enhanced anticorrosion properties. it has also been found that, in particular, compositions comprising a compounded mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and such a complex are substantially noncorrosive.

The normal tendency of oils to become oxidized and corrosive is definitely inhibited in the improved compositions of the invention. Metal surfaces in general are not corroded by contact with these compositions and internal combustion engine alloy bearings, in particular, are remarkably benefited. Bearings of silver and similar metals which, as stated above are increasingly important due to their presently expanded use in marine and railroad diesel engines, are not corroded by these compositions whereas conventional oxidation inhibited oils have severely pitted and corroded such bearings. The advantages of these improvemnnts are obtained in the compositions of this invention without loss of stability or detergency in the composition.

The complexes of boric acid are not only very ellective alone in the oils as primary inhibitors of oxidation but also function in combination with other antioxidants as auxiliary inhibitors. They are, in addition, remarkably effective as metal deactivators for the common bearing metals, such as copper and lead, which normally tend to accelerate the decomposition of lubricating oil compositions.

The boric acid complexes of the compositions according to this invention are prepared by the reaction of a mixture of boric acid and glycol or polyhydroxy benzene. The mixtures are ordinarily heated to accelerate the reaction. Although the nature of the reaction is not definitely known, it is believed that two of the hydroxyl groups of a single glycol or polyhydroxy benzene react with the boric acid to form what is commonly termed a metal chelate compound." These compounds are characterized by a claw" type of structure in which one or more rings of similar or unlike structure due to the use of mixed glycols or polyhydroxy benzenes are formed including the boron.

The glycols which are reacted with the boric acid are preferably alphaand beta-alkanediols containing from 2 to 18 carbon atoms. Such glycols include, for example, ethylene glycol, 1,2- and 1,3-propanediol, 1,3-pentanediol, 2,3-butanediol, 1,2-hexanediol, 2methyl-l,3-pentanediol, 1,2- and 1,3-octylene glycols including Z-ethylhexane- 1,3-diol, 1,2-dodecanediol, 2,4-diethyl-octane-1,3-diol, and 2,4,6-triethyl-decane-l,3-diol. The glycols containing from 6 to 10 carbon atoms are more preferred since they impart an optimum degree of oil solubility to the borate. Alphaand beta-octylene glycols such as Z-ethylhexane- 1,3-diol have been found to be the most satisfactory for present purposes since they give unusually eifective oxidation and corrosion inhibitors.

The polyhydroxy benzenes are preferably vicinal dihydric phenols such as catechol, 3,4-dihydroxy toluene, text.- butylcatechol, cetylcatechol, and the like. They may contain additional hydroxyl groups, as for example, 1,2,4-

trihydroxy benzene. Alkyl catechols containing from 2 to 18 carbon atoms in the alkyl group are at present most preferred since the borates prepared from them possess the most satisfactory oil solubility characteristics.

Although boric acid complexes suitable for use in the compositions of the invention may be prepared from either glycols or polyhydroxy benzenes of the type illustrated above. the complexes of boric acid with polyhydroxy benzenes are presently preferred. According to test results obtained to date. the latter compounds are several times more effective as corrosion inhibitors and antioxidants than the glycol borates.

Although it is convenient for the sake of illustration to refer to the reaction of boric acid with the glycol or polyhydroxy benzene or mixtures thereof to form the complexes for the lubricating oil compositions of this invention, other boric acid compounds may also be employed. Such compounds include boric anhydride, and boron trichloride.

The complex of boric acid with glycol or polyhydroxy benzene is present in the compositions of the invention in an amount at least sufiicient to inhibit corrosion or oxidation. Small amounts, usually from about 0.01 to about 5.0 percent by weight based on the oil, are effective. Proportions ranging from about 0.05 to about 1.0 percent are preferred in most lubricating oil compositions. Concentrates containing larger proportions, up to 50 percent, either in solution or suspension. are particularly suitable in compounding operations.

Any of the well known types of oils of lubricating viscosity are suitable base oils for the compositions of the invention. They include hydrocarbon or mineral lubricating oils of naphthenic, paraffinie, and mixed naphthenic and paraflinic types. They may be refined by any of the conventional methods such as solvent refining and acid refining. Synthetic hydrocarbon oils of the alkylene polymer type or those derived from coal and shale may also be employed. Alkylene oxide polymers and their derivatives such as the propylene oxide polymers and their ethyl esters and acetyl derivatives in which the terminal hydroxyl groups have been modified are also suitable. Synthetic oils of the dicarboxylic acid ester type including dibutyl adipate, di-Z-ethylhexyl sebacate, di-n-hexyl fumaric polymer, dilauryl acylate, and the like may be used. Alkyl benzene types of synthetic oils such as tetradecyl benzene. etc. are also included. Liquid esters of acids of phosphorus including tricresyl phosphate, diethyl esters of decane phosphonic acid, and the like may also be employed. Also suitable are the polysiloxane oils of the type of polyalkyl-. polyaryl-, polyalkoxyand polyaryloxy siloxancs such as polymethyl siloxane, polymethylphenyl siloxane and polymethoxyphenoxy siloxanc and silicate ester oils such as tetraalkyland tetraaryl silicates of the tetra-2-ethylhexyl silicate and tetra-p-tert.-butylphenyl silicate types.

In a preferred embodiment of the invention, as mentioned above, the complexes of boric acid with glycol or polyhydroxy benzene are employed in combination with compounded mineral lubricating oils of the internal combustion engine type which are normally corrosive to alloy bearings. In such an embodiment, as in the case of the other, straight oils of lubricating viscosity, at major proportion of the lubricating oil normally corrosive to metals and/or subject to oxidation and a small amount, sufficient to inhibit said corrosion and/or oxidation, of a boric acid complex provides a remarkably improved composition. These compounded oils customarily contain detergents such as the oil-soluble petroleum sulfonates and stabilizers such as the metal alkyl phenates. Other agents such as oiliness agents, viscosity index improvers, pour point depressants. blooming agents, peptizing agents, etc. may also be present.

In further illustration of the invention, the following examples are submitted showing the preparation of the boric acid complexes and evaluation of their effectiveness as corrosion inhibitors and antioxidants in oil composition. Unless otherwise specified the proportions given in these examples are on a weight basis.

EXAMPLE 1 A mixture of two moles of 4-tert.-butylcatechol and one mole of boric acid and 300 milliliters of toluene is refluxed with continuous water separation until the mixture be comes homogenous and Water evolution has ceased. Total Water evolved is 55.5 grams (3.1 moles) compared to a theoretical for di(4-tert.-butyl pyrocatechol) boric acid of 3.0 moles. The toluene is distilled off and the glassy product thus obtained is used directly in compounding lubricating oil compositions.

EXAMPLE 2 One mole of pinacone, otherwise known as 2,3-dimethyl- 2,3-butanediol is evaporated with a supersaturated aqueous solution of one mole of boric acid. The evaporation is carried out in a vacuum under sulfuric acid. The pinacone boric acid thus obtained is a crystalline solid melting at about 70 C.

EXAMPLE 3 One mole of 2,4 dimethyl 2,4 pentanediol is mixed with a hot concentrated aqueous solution of one mole of boric acid. The Water is removed by evaporation. The 2,4 dimethyl 2,4 pentanediol boric acid product is a stable compound melting at C. and boiling at 228 C. It is soluble in benzene.

EXAMPLE 4 One mole of 2,4 dimethyl 2,4 hexanediol is mixed with a hot concentrated aqueous solution of one mole of boric acid. The water is evaporated. The 2,4-dimethyl-2,4-hexanediol boric acid thus obtained is a solid material melting at 43 to 45 C. and soluble in petroleum ether.

EXAMPLE 5 One mole of boric acid is dissolved in two moles of 2-methyl-2,4-pentanediol by heating. Di-(2-methyl-2,- pentanediol) boric acid is thus obtained.

The effectiveness of the lubricating oil compositions of the invention is demonstrated by the copper-lead strip corrosion test. In this test a polished copper-lead strip is weighed and immersed in 300 cubic centimeters of test oil in a 400-milliliter lipless Berzelius beaker. The test oil is maintained at 340 F. under a pressure of one atmosphere of air and stirred with a mechanical stirrer at 1000 R. P. M. After two hours a synthetic naphthenatc catalyst is added, unless otherwise specified, to provide the following catalytic metals:

Percent by weight The test is continued 20 hours. The copper-lead strip is then removed, rubbed vigorously with a soft cloth and weighed to determine the net weight loss.

The test oils include both a mineral lubricating oil which is an acid refined mineral oil and compounded mineral lubricating oils of the internal combustion engine type which are normally corrosive to alloy bearings. The compounded oil (A) is a solvent refined SAE 30 mineral lubricating oil base containing 10 mM./l g. of neutral calcium petroleum sulfonate and 36 mM./kg. of calcium alkyl phenate, sulfurized. compounded oil (B) is a solvent refined SAE 40 mineral lubricating oil base having a viscosity index of 60 and containing 10 mM./kg. of neutral calcium petroleum sulfonate and ancsgscs 20 mM./kg. of calcium alkyl phenate, sulfurized. Compositions which comprise a major portion of a compounded oil of lubricating viscosity having a base reserve and a minor portion at least suflicient to enhance the resistance of said oil base depletion due to oxidation of a complex of the above type constitute another embodiment of this invention. Such base reserve" oils contain additives such as basic alkaline earth metal sulfonates, alkaline earth metal alkyl phenates, alkaline earth metal salts of hydroxy phenyl sulfides and disulfides, etc. in amounts to give the composition a pH on the alkaline side, i. e., 10 or so. Ordinarily, 0.01 to 10.0% is sufiicient. The proportions of boric acid complex apply here as mentioned above.

The results of the test are shown in the following table. The concentrations of boric acid complex employed are given in either millimoles of boron per kilogram of oil or percent by weight of the composition.

Table I COPPER-LEAD STRIP CORROSION TEST Copper- Lead Additive Base Oil Stri Welg t Loss (ma) Noneno catalyst Mineral lub. oil 84. 4 40 mM./kg. 4-t-bntylcatecho1 bo- Same 2.0

rate-no catalyst. 30 mMJkg. catechol bornteno Same 12.9

catalyst. 30 mMJkg. ditethylene glycol) bo- Same 245.0

rate-no catalyst. None Oomponnded oil (AL. 160. 1%7 idi(4-tt=:rt.-butyl pyrocatechol) Same 50.0

or c a 2.0% di(4-tert.-butyl pyrocatechol) 4.0

boric acid. 2.0% dl-pyrocatechol borlc acid 0.0 207301 ?rethylhexane-l,3-diol boric 109.0

ac 4.07,;d 2-ethylhexane-1,3-diol boric 50.0

ac 0.5% zethylhexane-lfi-diol pyro- Same 100.0

catechol boric acid. N oneno catalyst compounded 011 (B) 22. 0 1.0% di(4-tert.-butyl pyrocatechol) Same l.0

boric acid-no catalyst. 2.0% di(hexylene glycol) boric acld- Same 7. 0

no catalyst. 2.0% hexylene glycol boric ncldno Same 2. 0

catalyst. None Oompounded oil (13).. 200. 0 1.0% di(4-tert.-butyl pyrocatechol) Same 4.0

horic acid.

As shown by the above test data, straight mineral lubricating oil alone gives a copper-lead strip weight loss due to corrosion of over 84 milligrams in the 20-hour period. By Way of distinction, compositions in accordance with this invention containing the same straight mineral lubricating oil base and borate corrosion inhibitors give as little as 2.0 milligrams weight loss. In the case of the conventional compounded mineral lubrieating oils of the internal combustion engine type which are normally corrosive to copper-lead bearings, the improvement is even more remarkable. The various compounded oils alone give copper-lead strip weight losses ranging as high as 200 milligrams whereas the lubricating oil compositions of the invention containing the same compounded base oil plus a glycol or polyhydroxy benzene complex of boric acid result in very little or no corrosion loss.

The lubricating oil compositions of the invention are also evaluated for their efiectiveness in a modified copper-lead strip corrosion test. This test is similar to that described above but is modified to simulate removal of corrosion products by the wiping action on the bearings in the engine. A new copper-lead strip is introduced every four hours and the accumulative weight loss is recorded. Compounded oil (B), the reference oil, is the same as described above. Illustrative test results are as follows:

The above test results show that the lubricating oil compositions of the invention are effective as corrosion inhibitors even in situations where protective surface films may be wiped oil the metal surface as, for example, by the wiping action on hearings in an engine.

The performance characteristics of the lubricating oil compositions of this invention are also illustrated by their evaluation in a number of engine tests. The engine test procedures and techniques, though conventional and well known in the lubricating oil art, are briefly described for the sake of convenience in the following paragraphs along with the test data.

In the L-4 engine test the corrosion characteristics of the oils are determined in a Chevrolet standard 6-cylinder engine in a typical laboratory installation. Weighed copper-lead test bearings and new piston rings are installed. The test is run at a constant engine speed at about 3000 R. P. M. under a load of 30 brake horse-power for a total of 36 hours subsequent to a run-in period of 8 hours. The outlet temperature of the jacket coolant is 200 F. and the oil sump temperature is 280 F. At the conclusion of the test the engine is disassembled and inspected for varnish and sludge deposits and the various parts are rated on a cleanliness scale of 0 to 10. The bearings are weighed to determine the weight loss per whole bearing due to corrosion. Illustrative test results on the compositions of the invention using a compounded oil containing 7 mM./kg. of neutral calcium petroleum sulfonate and 16 mM./ kg. of calcium alkyl phenate, sul- There is very little viscosity increase in the test oil. The piston rating is in excess of 9 on a cleanliness scale of 0 to 10 and the total engine varnish and sludge deposit rating exceeds on a scale of 0 to 100. Not only is the test oil of the composition according to the invention effective in reducing the bearing corrosion loss from more than 500 milligrams to milligrams per whole bearing but it also gives a very high performance rating so far as engine cleanliness and varnish and sludge deposits are concerned.

In the L-l engine test the detergency and wear inhibiting characteristics of the lubricating oil compositions of the invention are evaluated in a single cylinder caterpillar diesel test engine. The piston rings, cylinder liner, valves, etc. are standard production units of the diesel type. The engine is operated at a speed of 1000 R. P. M. under a load of approximately 20 brake horse-power. The outlet jacket temperature of the coolant is 175 to 180 F. and the oil temperature to the bearings is to F. After 120 hours operation with 0.4 percent sulfur-containing fuel, the engine is inspected for cleanliness. The reference oil is the same as described above. Illustrative test data are set out in the following table.

Table I V Oil Engine Conditions Reference of] Clean, 2.0% (iit'i-terL-butyl pyrocatechol) boric acid Clean.

The above test data show that the lubricating oil compositions of the invention are excellent diesel engine lubricating oils of the heavy duty type.

The Ll and L-4 engine tests referred to above are more fully described in the C. R. C. Handbook, 1946 edition, Coordinating Research Council, New York, New York.

In the Navy propulsion load test described in Mil. Pl7269 (Ships) July 17, 1952, the compositions of the invention are evaluated as diesel engine lubricating oils under severe operating conditions. The tests are run in a General Motors 4-cylinder diesel engine using one percent sulfur fuel. Copper-lead bearings are employed. The tests are run at a constant speed of 1800 R. P. M. under a load of 30 brake horse-power per cylinder. The crankcase temperature is 250 F. The present test is run continuously to simulate railroad diesel engine performance unlike the standard Navy test procedure which permits regular 4-hour shutdown periods. Sea water was also excluded for the same reason. The reference oil is a solvent refined SAE 40 mineral lubricating oil base having a viscosity index of 60 and containing 10 mM./kg. of neutral calcium petroleum sulfonate and 20 mM./kg. of calcium alkyl phenate, sulfurized. Test results are as follows:

Table V Weight Loss, rugs/Whole Bearing Hours) Oil Reference 00...... 70 S30 2, 000 H 2.0"; di(2metliyl-ZA-pentanediol) horic acid in reference oil.... .10 470 1.200 0.25% iZ-ethyl-l,3-lzexunedioi pyroentcehol boric acid in reference oil 200 1. 200 0.50;. di(-i-tert.-butyl pyrocatccllol) horic acid in reference oil I 0 0 180 780 2.0% di(-l-tert.-butyl pyrocateehoi) borie acid in reference oil .7 0 0 00 250 In the Navy propulsion load test results shown above, the bearing weight loss due to corrosion by the reference oil, a conventional heavy duty compounded oil, was extremely high. Such an oil would be impossible to use for any prolonged period of time without shutdown. By way of distinction, the lubricating oil composition of the invention containing borate complexes gives remarkably low corrosion losses after as much as 200 hours of continuous operation. Greatly extended periods of uninterrupted operations of diesel engines are thus possible with these improved oils.

In a similar Navy engine test employing the silver bearings which are being more and more frequently applied in diesel engines having highly loaded bearings, compositions of the invention containing borate complexes are found to give effective lubrication throughout long periods of uninterrupted operation with very low weight loss of the silver bearing. 0n the other hand, conventional oxidation and corrosion inhibited lubricating oil compositions compounded with sulfur-containing additives such as zinc diaikyl dithiophosphate and sulfurized diparaffin sulfide are entirely too corrosive toward silver bearings. It is a further fact. aside from bearing corrosion. that silver metal-containing bearings are extremely sensitive to lubricant compositions containing sulfur type additives and such compositions generally provide an unsatisfactorily low degree of lubricity for the silver surfaces.

The effectiveness of the lubrication oil compositions of the invention as antioxidants is also determined in the series of oxidation tests in which the base depletion by oxidation is measured. In these tests the oil is maintained at a temperature of 340 F. under a pressure of one atmosphere of oxygen. During the test the oil is agitated by a high-speed glass stirrer and the amount of oxygen added to maintain the pressure at one atmosphere is recorded. Unless otherwise noted, no oxidation catalyst is employed.

In the first method of determining base depletion by oxidation, 25 grams of the oil are oxidized according to the above procedure until 200 cubic centimeters of oxygen have been absorbed. A S-gram sample of the oil is then titrated with standard 0.01 Normal hydrochloric acid to determine the number of cubic centimeters of acid necessary to give a pH of 7, 6 and 5. The time of oxidation required to absorb 200 cubic centimeters of oxygen is also recorded. The reference oil is a solvent refined SAE 30 mineral lubricating base oil containing 10 mM./kg. of neutral calcium petroleum sulfonate and 36 mM./kg. of calcium alkyl phenate, sulfurized. lllustrative test results are given in the following table.

Table VI Cubic Centimeter,

Acid to pH Time of Oil Oxidation (Hours) 7 6 5 Reference oil 0.0 1.0 3.3 11.3 2.0% mono (2 methylpentane 2,4-dioi) boric acid in reference oii 3. 4 6. 7 10. 2 12. 5 0.5% 2ethylheXane-l,3-di0l pyrocatechol boric acid in reference oil... 0.2 2. 7 5. J 14. 5 2.0% 2-ethylhexane-l,3-dio1 p use i boric acid in reference oil 0. 5 3. 4 7. 2 12. 5 0.5% di-(tert.-butyl pyrocatechol) boric acid in reference 011 1.. 8 4. 7 8. 1 11.5 2.0% di(tert.-butyi pyrocatechol) boric acid in reference oil 6. 2 11.4 10. 4 7. 3 Reference oil plus 0.5% iron naphthenato I catalyst 0.0 1. 3 4. t5 4. 9 2.0% rli-(tert.-butyl pyrocatechoi) boric acid in reference oil with catalyst 11.1 1 15. 5 i9. 5 0.0

From the test results of the above table, it is seen that the compositions of the invention containing various glycol and polyhydroxy benzene borate complexes exhibit improved resistance to base depletion by oxidation. Although only 3.3 cubic centimeters of 0.01 Normal hydrochloric acid are needed to titrate 5 grams of the reference oil to a pH of 5, much larger amounts ranging as high as 16.4 cubic centimeters are required to reduce similar samples taken from the inhibited compositions of the in vention.

In another method of evaluating the antioxidant effect of the lubricating oil compositions of the invention, the oil is oxidized by the method outlined above except that S-cubic centimeter samples are withdrawn at various time intervals and titrated with 0.01 Normal hydrochloric acid to a pH of 5. 0.05% of iron naphthenate catalyst is employed. The reference oil is an SAE 30 solvent refined mineral lubricating oil base with 10 mM./kg. of neutral calcium petroleum sulfonate and 20 mM./kg. of calcium alkyl phenate, sulfurized. Illustrative test results are given in the following table.

Table VII Time Oxidized (Minutes) 011 In the above test results the borate complex containing lubricating oil compositions of the invention are shown to have greatly improved resistance to oxidation compared to uninhibited lubricating oil compositions. Furthermore, the antioxidant effect of the present compositions even exceeds that obtained when some of the very best antioxidants known to the art, such as di-n-butylamino methyl phenol and phenyl-a-naphtbylamine, are employed.

In still another method of determining the antioxidant effect of the present compositions, samples of the oil are taken from the Navy propulsion load test described above. These samples are taken at various time intervals and tested to determine their pH by titrating with 0.01 Normal hydrochloric acid. The reference oil is an SAE 40 solvent refined mineral lubricating oil base having a viscosity index of 60 and containing 10 mM./kg. of neutral calcium petroleum sulfonate and 20 mM./kg. of calcium alkyl phenate, sulfurized. Illustrative results As shown by the above test results, improved antioxidant properties are found in the compositions of the invention when evaluated in actual engine tests. Longer periods of uninterrupted operation of diesel engines are possible with the borate inhibited compositions compared to uninhibited compositions before the base reserve is depleted to a pH of 5.

The antioxidant properties of the lubricating oil com positions of the invention are also evaluated in tests for determining the oxidation inhibition period. In these tests the oil is contained in a large glass tube equipped with a high-speed glass stirrer. The oil temperature is 340 F. and a pressure of about one atmosphere of pure oxygen is maintained. The volume of oxygen added is automatically recorded and the time in hours required for 100 grams of oil to absorb 1200 cubic centimeters of oxygen is called the inhibition period. Illustrative test results are as follows:

Table IX Oil cid refined white mineral all (reference oil) .17 phenyl-a-naphthylamine in reference oil t-t-butylcatechol in reference oil pentaerythritol monooleate borate in reference oil...

o Hz-but lcatechol borate in reference oil .5 2-ethy exanediol-1,3 borate in reference oil. .1 butanedlol-2,3 borate in reference oil 0.5% peutaerythritol monooleate borate and 0.1% phenyl-anaphthylamine in reference 011 0.5% pentaerythritol monooleate borate and 0.2% 4-15- "l%ii i i W t an; "a t uycaec o oree an .1 a p eny-a-nap t ylmnine in reference 011 0.6% 2-ethylhexanedtol-L3 borate and 04% phen naphthglarnlne in reference 011 0.5% 2-et ylhexanedlol-Ltt borate and 0.2% 4-t-butylcatechol in reference 011 0.1% butanediol-2,3 borate and 0 1% phenyl-a-naphthylamine in reference oil 0.17 butanediol-2,3 borate and 2% erence 011 The test data of the above tables show that lubricating oil compositions containing the complexes of the invention may be efiectively inhibited against oxidation where'- as similar lubricating oil compositions without the boric acid complexes are susceptible to a very high rate of oxidation. The test results of the above tables also show that when conventional oxidation inhibitors of the diary] amine and polyhydroxy benzene type illustrated by phenylu-napthylamine and 4-t-butylcatechol, respectively, are employed in the compositions according to this invention, a marked improvement in the efiect of the primary oxidation inhibitor is obtained, indicating synergism of the conventional antioxidant and the borate. This improvement is particularly noticeable when the preferred diaryl amine type of primary oxidation inhibitor is employed in combination with either glycol type borates or catechol type borates.

Other conventional oxidation inhibitors of the diaryl amine type which are suitable for employment in the improved compositions of the invention include p-hydroxy diphenyl amine, p,p-dihydroxy diphenyl amine, diphenylp-phenylene diamine, diphenyl amine, phenothiazine, difl-naphthylamine, etc. Other polyhydroxy aromatic compounds include 1,2-dihydroxy naphthalene, hydroquinone, di-t-butyl-resorcinol, 1,2-dihydroxy-4amino naphthalene, etc. Other oxidation inhibitors of these general types are also well known in the art.

In the compositions of the invention including both conventional oxidation inhibitors and the borate, any amount of the conventional inhibitor sufficient to inhibit oxidation and any amount of the borate sufficient to enhence the action of the conventional inhibitor may be employed. Ordinarily, amounts of from 0.1 to 5.0 percent by weight of the composition of the conventional inhibitor and the borate each are suflicient. Preferably from 0.05 to 2 percent by weight of each inhibitor is employed in operations where there is little danger of encountering extremely high temperatures. The amounts of conventional inhibitor and borate need not be the same in any given composition.

The nature of the improved lubricating oil compositions of the invention and their efiectiveness should be readily apparent from the many illustrations given above. Oxidation and corrosivity in the compositions are definitely inhibited to a very substantial degree. Particularly corrodible metals such as engine alloy bearings of copper, lead, and the like, as well as bearings of silver, are not adversely affected. This is indeed remarkable since the problem of devising lubricant compositions uniformly noncorrosive to both types of bearing metals has long confronted workers in the art. As shown by the actual tests set out above, the advantages of these improvements are obtained without loss of other desirable properties of the lubricant compositions.

As mentioned above, the boron compounds of the compositions according to this invention are preferably formed from boric acid and an alphaor beta-diol or vincinal dihydroxy benzene. Although the present invention is in no way limited to any theory concerning the structure of the compounds, it is believed that they may be illustrated by the following formulae:

Di-glycol borntec 1 Mono-glycol borate! \B/ so Mono-pyrocatechol borates Di-(pyrocatechol) borntes wherein R is hydrogen or a group of hydrocarbon structure as previously described.

Although the above types of compounds are distinctly preferred in the compositions of the invention, other compounds of similar structure having substituents on the hydrocarbon groups which do not adversely affect the reaction may likewise be employed. Such substituents include: hydroxyl groups, as when a polyhydroxy alcohol or benzene such as glycerol, pentaerythritol, sorbitol or t'rihydroxy benzene is used; ester groups, as when glycerol monooleate or sorbitan monooleate is used; and halogens, ethers, amides, etc., as will be apparent to those skilled in the art from the above description of the invention.

Although the compositions of the invention have been primarily described as crankcase lubricants for internal combustion engines, they are also useful as turbine oils, hydraulic fluids, instrument oils, constituent oils in grease manufacture, ice-machine oils, and the like.

We claim:

1. A lubricant composition consisting essentially of an oil of lubricating viscosity and a member of the group consisting of borates of alphaand beta-glycols of 2 to 18 carbon atoms and 4-tert.-butyl pyrocatechol in an amont sutficient to inhibit corrosion.

2. A lubricant composition consisting essentially of an oil of lubricating viscosity and a borate of an alphaalkanediol of 2 to 18 carbon atoms in an amount sufficient to inhibit corrosion.

3. A lubricant composition consisting essentially of an oil of lubricating viscosity and a borate of a beta-alkanediol of 3 to 18 carbon atoms in an amount sufiicient to inhibit corrosion.

R ID

4. A lubricant composition consisting essentially of a mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and a member of the group consisting of borates of alphaand betaglycols of 2 to 18 carbon atoms and 4-tert.-butyl pyrocatechol in an amount sufiicient to inhibit corrosion.

5. A lubricant composition consisting essentially of mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and a borate of an alpha-alkauediol containing from 2 to 18 carbon atoms in an amount sufficient to inhibit corrosion.

6. A lubricant composition consisting essentially of a mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and a borate of a beta-alkanediol containing from 3 to 18 carbon atoms in an amount sufficient to inhibit corrosion.

7. A lubricant composition consisting essentially of a mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and from about 0.01 to about 5.0 percent by weight based on the oil of a borate of 2-ethylhexane-l,3-diol.

8. A lubricant composition consisting essentially of a mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and from about 0.01 to about 5.0 percent by weight based on the oil of a borate of 4-tert.-butyl pyrocatechol.

9. A lubricant composition consisting essentially of a mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and from about 0.01 to about 5.0 percent by weight based on the oil of a borate of ethylene glycol.

References Cited in the file of this patent UNITED STATES PATENTS 2,144,654 Guthmann et al Jan. 24, 1939 2,161,184 McKone et al June 6, 1939 2,305,627 Lincoln et al Dec. 22, 1942 2,410,652 Gritfin et al Nov. 5, 1946 2,465,296 Swiss Mar. 22, 1949 2,497,521 Trautman Feb. 14, 1950 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF AN OIL OF LUBRICATING VISCOSITY AND A MEMBER OF THE GROUP CONSISTING OF BOROATES OF ALPHA-AND BETA-GLYCOLS OF 2 TO 18 CARBON ATOMS AND 4-TERT.-BUTYL PYROCATECHOL IN AN AMOUNT SUFFICIENT TO INHIBIT CORROSIN. 